Sennheiser SR 3254 - Manual (Page 27)

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Additional information
HDX noise reduction
Progress you can hear:
The product family is equipped with HDX , the Sennheiser noise
reduction system that reduces RF interference. It increases the
signal-to-noise ratio in wireless audio transmission to more
than 90 dB.
HDX is a wideband compander system which compresses the
audio signal in the transmitter in a 2:1 ratio (related to dB) to
lift it above the inherent noise floor of the RF link. In the receiver
the signal is expanded in an identical and opposite way in a 1:2
ratio to restore the original signal, at the same time reducing
the RF noise to below the noise floor of the receiver.
HDX has been specially developed for high quality radio
microphone systems.
Note:
Only transmitters and receivers that are equipped with HDX
can work correctly with each other. If non HDX equipment
was mixed with
HDX , the dynamic range would be
drastically reduced and the transmission would sound blunt
and flat.
RF link
Transmitter Receiver
Inherent
noise of
the RF link